The albumins of Chinook salmon (Oncorhynchus tshawytscha) and brown trout (Salmo trutta) appear to lack a propeptide.
Plasma samples from two members of the Salmonidae family, the chinook salmon (Oncorhynchus tshawytscha) and brown trout (Salmo trutta), were examined. Albumin, initially identified as the predominant anionic palmitate-binding band on agarose gel electrophoresis of plasma, was purified from both species by DEAE-ion exchange chromatography. Albumin has a plasma concentration of approximately 15 mg/ml in both species. Like other fish species, neither trout nor salmon albumin binds nickel; a characteristic of many mammalian albumins. Salmon and trout albumins have molecular masses of 65 and 67 kDa, respectively, indicating some sequence differences. However, N-terminal sequencing of the first 15 residues of both these proteins indicated identical sequences of 1QNQICTIFTEAKEDG15-. This showed that the mature N-terminal sequence (SQAQNQICTIFTEAKEDG-) predicted from the cDNA of Atlantic salmon albumin is in fact incorrect, with the actual N-terminus for salmonids starting three amino acids later than that predicted. Examination of the Atlantic salmon cDNA sequence suggested that salmonid albumin is unique, in lacking a propeptide. No proalbumin convertase site (RXYR/XYRR) is present and it appears that the salmonid albumin precursor is cleaved only by the signal peptidase, between -1 Ala and +1 Gln, to produce mature albumin. This site has a preferrred motif for the signal peptidase of -1 Ala and -3 Ser, as well as -2 Gln. Thus, salmonid albumin possesses a 21-residue prepeptide, but no propeptide.
Metcalf
V
V
Department of Pathology, University of Otago, Christchurch, New Zealand. vmetcalf@chmeds.ac.nz
Brennan
S
S
Chambers
G
G
George
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001798:Blood Proteins / Q000032:analysis / Q000737:chemistry*; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D008970:Molecular Weight; D011228:Prealbumin / Q000737:chemistry; D011499:Protein Processing, Post-Translational / Q000502:physiology; D012474:Salmon / Q000097:blood*; D017421:Sequence Analysis; D012697:Serine Endopeptidases / Q000378:metabolism; D014337:Trout / Q000097:blood*
D001798:Blood Proteins; D008565:Membrane Proteins; D011228:Prealbumin; D012697:Serine Endopeptidases; C026515:type I signal peptidase